Michael is 3 times as old as Tiffany. Twelve years ago, Michael was 5 times as old as Tiffany. How old is Tiffany now?
Explanation: We can use the given information to write down two equations that describe the ages of Michael and Tiffany. Let Michael's current age be $m$ and Tiffany's current age be $t$ The information in the first sentence can be expressed in the following equation: $m = 3t$ Twelve years ago, Michael was $m - 12$ years old, and Tiffany was $t - 12$ years old. The information in the second sentence can be expressed in the following equation: $m - 12 = 5(t - 12)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $t$ , it might be easiest to use our first equation for $m$ and substitute it into our second equation. Our first equation is: $m = 3t$ . Substituting this into our second equation, we get: $3t$ $-$ $12 = 5(t - 12)$ which combines the information about $t$ from both of our original equations. Simplifying the right side of this equation, we get: $3 t - 12 = 5 t - 60$ Solving for $t$ , we get: $2 t = 48.$ $t = 24$.